The air compressor component of turbochargers has evolved through decades of design and development with a goal of maximizing efficiency and flow range, while minimizing the turbocharger rotational inertia. The rotating assembly of a turbocharger consists of the turbine wheel mounted on a first end of a shaft combined with the compressor wheel positioned on the opposite end of the shaft. The shaft is supported by a bearing system in between the two wheels.
In operation, the turbine wheel accepts engine exhaust gas and provides the horsepower to drive the rotating assembly. The spinning of the compressor wheel induces air communicated from the atmosphere through an air cleaner and compresses it. The stream of compressed air is communicated through a compressor casing from which it is delivered to the engine intake manifold.
The acceleration rate of the rotating assembly of a conventional turbocharger, depends on the rotational inertia of the rotating assembly and the friction losses in the bearing system. In operation, engaged with a vehicle to boost engine power, conventional turbochargers work well at engine speeds above idle, but are prone to “turbo lag” which occurs when the engine moves from an idle to accelerate. To minimize the so-called “turbo lag” when the engine throttle is opened to accelerate a vehicle, the rotational inertia of the turbocharger rotor must be minimized. Since the compressor wheel is a vital component of the turbocharger rotor, its inertia must be minimized while, at the same time, the performance of the compressor must be maintained at as high a level as possible. Thus, to minimize the inertia of the small-size compressor wheels employed in automotive turbochargers which conventionally have a minimal size (under 5″ in diameter), the number of radial positioned compressor vanes are kept low and the mass of the wheel hub must be as low as possible.
To comply with the restrictions noted above, compressor wheel design has evolved over the years to be of a relatively short length, and be formed with a low number of backward-leaning compressor vanes with sharp leading edges. With proper attention paid to the airflow path running through the wheel passages, and to the design of the diffuser outboard of the wheel, efficiencies of up to 80% are conventionally being achieved. Due to the many years of development and refinement of design methods which have contributed to reaching this high level of efficiency, it is doubtful if further increases in compressor efficiency can be achieved through wheel design alone.
As such, there is an unmet need for a device and method which can improve the performance of conventional turbochargers. Such a device should be employable as a component in newly manufactured turbochargers, as well as be adapted for retrofit engagement to existing turbochargers to provide improvement in performance.